The audio and multimedia industries have continually strived to overcome the imperfections of reproduced sound. For example, a common imperfection is that the recording of sounds emanating from multiple locations is not properly reproduced in an audio system. One approach directed to improving the reproduction of sound includes surround sound systems which have multiple recording tracks. The multiple recording tracks are used to record the spatial information associated with sounds which emanate from multiple locations.
For example, in a surround sound system, some of the recording tracks contain sounds which are intended to originate from in front of the listener, while other recording tracks contain sounds which are intended to originate from behind the listener. When multiple speakers are placed around the listener at positions representing the intended origin of the recorded sounds, the audio information contained in the recording tracks makes the produced sounds appear more realistic to the listener. Such systems, however, are typically more expensive than systems which do not use multiple recording tracks and multiple speaker arrangements.
To conserve costs, many conventional two-speaker systems attempt to simulate a surround sound experience by introducing unnatural time-delays or phase-shifts between left and right signal sources. Unfortunately, such systems often suffer from unrealistic effects in the reproduced sound.
Other known sound enhancement techniques operate on what are called "sum" and "difference" signals. The sum signal, which is also called the monophonic signal, is the sum of the left and right signals. This can be conceptionalized as adding or combining the left and right signals (L+R).
The difference signal, on the other hand, represents the difference between the left and right audio signals. This is best conceptionalized as subtracting the right signal from the left signal (L-R). The difference signal is also often called the ambient signal.
It is known that modifying certain frequencies in the difference signal can widen the perceived sound projected from the left and right speakers. The widened sound image typically results from altering the reverberant sounds which are present in the difference signal. Sound enhancement techniques which process sum and difference signals is disclosed in U.S. Pat. Nos. 4,748,669 and 4,866,774, both issued to Arnold Klayman, one of the inventors for the invention disclosed in the present application.
In existing sound enhancement systems which process the sum and difference signals, the sum and difference signals are generated from circuitry which combines the left and right input signals. In some systems, once the circuitry generates the sum and difference signals, additional circuitry then separately processes and recombines the sum and difference signals in order to produce an enhanced sound effect. For example, the sound system disclosed in U.S. Pat. No. 4,748,669 has a sum and difference signal generator. Also, the sound system disclosed in U.S. Pat. No. 4,308,423 has a difference signal generator.
Typically, the creation and processing of the sum and difference signals are accomplished with digital signal processors, operational amplifiers and the like. Such implementations usually require complicated circuitry which increases the cost of such systems. Thus, despite the contributions from the prior art, there exists a need for a simplified audio enhancement system which reduces costs associated with producing an enhanced listening experience.